#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>

int main()
{

	int arr[] = { 1,2,3,4,5,1,2,3,4 };
	int sz = sizeof(arr) / sizeof(arr[0]);
	int a = arr[0];
	int i = 0;
	for (i = 1;i < sz; i++)
	{
		a ^= arr[i];
	}
	printf("%d\n", i);
	return 0;
}